The present invention relates to variable displacement compressors that are used, for example, in vehicle air conditioners. More particularly, the present invention pertains to a displacement control valve for controlling displacement of a variable displacement compressor.
A typical variable displacement compressor includes a drive shaft that is rotatably supported in its housing. The housing includes a cylinder block having cylinder bores. Each cylinder bore reciprocally houses a piston. A crank chamber is also defined in the housing. The crank chamber accommodates a swash plate. The swash plate is supported on the drive shaft to rotate integrally with and to tilt with respect to the drive shaft. Rotation of the swash plate reciprocates the pistons thereby causing the pistons to draw refrigerant gas from a suction chamber into the cylinder bores and to compress the gas. The pistons then discharge the compressed gas from the cylinder bores to a discharge chamber.
The crank chamber is connected with a suction chamber by a bleeding passage. The bleeding passage includes a displacement control valve. The control valve regulates the bleeding passage for controlling the amount of refrigerant gas supplied from the crank chamber to the suction chamber thereby controlling the pressure in the crank chamber. Changes in the pressure in the crank chamber alter the pressure difference between the crank chamber and the cylinder bores. The alteration of the pressure difference changes the inclination of the swash plate. Accordingly, the displacement of the compressor is varied.
Japanese Unexamined Patent Publication No 5-172049 discloses such a displacement control valve. As shown in FIG. 7, a control valve 111 is accommodated in a hole 119a formed in the housing 119 of a compressor. The hole 119a functions as a part of a bleeding passage 118 that connects a crank chamber 115 with a suction chamber 120. The control valve 111 is therefore located in the bleeding passage 118. The control valve 111 has a cylindrical cover 112. The cover 112 defines a pressure sensing chamber 113. The pressure sensing chamber 113 is connected to the crank chamber 115 by pressure introduction holes 114. A pressure sensing member, or bellows 116, is housed in the pressure sensing chamber 113 and is coupled to a valve body 117. The bellows 116 moves the valve body 117 based on the pressure of refrigerant gas introduced into the pressure sensing chamber 113 from the crank chamber 115. In this manner, the control valve 111 controls the flow rate of refrigerant gas in the bleeding passage 118.
When mating the control valve 111 with the housing 119, the cover 112 is first inserted in the hole 119a. The cover 112 may hit the opening and the inner wall of the hole 119a. This may deform the cover 112. Deformation of the cover 112 may displace the bellows 116 from a predetermined position in the cover 112. The responsiveness of the valve body 117 to the pressure in the chamber 113 is determined by the position of the bellows 116 in the cover 112. Thus, if the bellows 116 is displaced from the predetermined position, the desired operational characteristics of the control valve 11 are not obtained. As a result, the displacement of the compressor is not accurately controlled. The displacement of the bellows 116 also hinders the movement of the bellows 116 and the valve body 117.